Study guide for final portion of course

what is a pre-programmed response?

Answer: a late component of a stretch reflex that occurs ~40ms after perturbation is applied - consists of M2/3 amplitudes that are much larger than the preceding M1 (monosynaptic reflex) amplitude

when is M2/3 large vs small?

Answer: large= when told to resist/oppose perturbation - M2/3 is large and blends in with volitional response that follows small=when told to relax/let go upon perturbation - no volitional response follows **for both,M1 is similar

Klippel-Feil Syndrome -what is it ? -what is observed in these patients for a pre-programmed response?

Answer: characterized by a webbing of the neck due to fused cervical vertebre - leads to bilateral projections from the cortex -when EMG recordings made from both arms, M1 observed only in ipsilateral arm but M2 and M3 observed contralaterally too= evidence of transcortical component of pre programmed response

what is M2/3 dependent on?

Answer: the specific task/set/instruction given - accomplished by descending inputs that project in spinal MN pool

evidence of spinal control in locomotion

Answer: 1.despite lesions in cerebral hemispheres (decerebrate)= ability for locomotion was not abolished - seen by stimulating midbrain locomotive region =able to evoke walking 2. stepping in chronic cat=also when EMG recorded of cats walking on treadmill = observed alternating contractions i.e: knee and ankle flexors working together, while knee and hip flexors worked tgt -there was reciprocal inhibition going on between the flexors and extensors —even observed 20 days after spinal cord lesions =evidence of central pattern generator 3. humans with spinal cord lesions, when shock administered, produced reciprocal movements of legs in bed

half centre model

Answer: proposed that flexors and extensors inhibit each other in a reciprocal manner in order to give rise to alternating/rhythmic stepping movements = network of interneurons in SC exists that drives rhythmic pattern of locomotion, independent of brain ex: excitatory interneurons of flexor muscles told to fire AP= while this burst is being sent to flexor MN, also has connections to interneuron in spinal cord, synapsing with an EPSP on contralateral extensor half centre= creates IPSP on inhibitory interneuron of contralateral extensor and prevents opposite side from coming on during flexion - recurrent loop on inhibitory interneuron, turns off flexor, allowing contralateral side to build its activity and do the same process on its side =this occurs in an alternating pattern between the sides

Evidence of CPGs in humans

Answer: when ~8month old baby is held for balance support on treadmill (not yet knowing how to walk independently), as treadmill moves, baby is seen to produce rhythmic, locomotive movements =evidence that scaffold for locomotion exists in spinal cord even at this time and although baby doesn\'t consciously know what it\'s doing, its spinal cord knows

importance of sensory feedback (4)

Answer: 1. initiating walking (brush cat on back, begins to walk) 2. controlling phase transitions= stance to swing 3. regulating level of muscle acitivty = shifting to stand on one leg 4. correcting unexpected disturbances = such as stumbling responses such as when slipping

controlling phase transitions mechanism

Answer: swing begins with flexion of the knee, hip and ankle flexors - then midway, as body weight begins to transfer, knee and ankle begin to extend via unloading of extensor muscles as leg moves ahead of the body, there is anticipation of weight about to be bared - these proprioceptive inputs can initiate walking

evidence of CPG —paper drum study

Answer: -showed rhythmic bursts of activity in stepping is generated by a network of neurons located in the spinal cord -proposed that contraction of flexion/extension muscles during stepping was controlled by 2 systems of neurons known as half centers in spinal cord when dorsal roots cut (so no sensory info is received from limbs), rhythmic alternating contractions were shown of the tibialis anterior and gastrocnemius (extensor muscles) occured right after transection of spinal cord